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Posted May 24, 2004

MDX in Analysis Services: Mastering Time: Change across Periods - Page 3

By William Pearson

Handling Period Comparisons at Numerous Levels

In this article, we will focus on period-related comparisons. By "period," I mean general levels of the time hierarchy, and not strictly months (some accounting systems refer to months as "periods"). Periods can be days, weeks, months, quarters, years, and others that occur between and external to these.

In addition, we will pursue a solution that handles a requirement to compare periods, but does so in such a way that the comparison will occur at all relevant levels. We will do this within the frame of an exercise where we build the MDX from scratch to meet a hypothetical business requirement, so that we can assimilate the concepts in a logical fashion, and see the working components in meaningful increments, rather than examining an omnibus query that requires the "distraction of dissection" that many of us have come to despise in today's pop technology media.

Let's take a look at a scenario that illustrates a need for a period-to-period comparison, using a hypothetical business need to add practical value. Let's say that a group of information consumers within the FoodMart organization have approached us with a need that they wish to meet using data that is housed within the Warehouse cube. The consumers want to be able to report upon the change in Warehouse Sales from month to month, but also want the ability to see the same delta at the quarter, semi-annual and annual levels of the Time hierarchy for year 1997.

We will approach this in steps, beginning with the following, and using our old friend, the Sample Application, as a platform from which to perform our practice exercises.

1.  Start the MDX Sample Application.

We are initially greeted by the Connect dialog, shown in Illustration 1.

Illustration 1: The Connect Dialog for the MDX Sample Application

The illustration above depicts the name of my server, MOTHER1, and properly indicates that we will be connecting via the MSOLAP provider (the default).

2.  Click OK.

The MDX Sample Application window appears.

3.  Click File --> New.

A blank Query pane appears.

4.  Ensure that FoodMart 2000 is selected as the database name in the DB box of the toolbar.

5.  Select the Warehouse cube in the Cube drop-down list box.

The MDX Sample Application window should resemble that depicted in Illustration 2, complete with the information from the Warehouse cube displaying in the Metadata tree (left section of the Metadata pane).

Illustration 2: The MDX Sample Application Window (Compressed View)

We will begin creating our query with a focus on building the Time hierarchy we need into the row axis, with the single Warehouse Sales measure, initially returning the "direct pulls" that require no calculated members. We will then add the additional Time aggregations we need, in the next step. Finally, in the last enhancements to the core query, we will add a calculated member, which we will call "Delta-to-Last," meaning "change over the last period." Delta-to-Last will reflect the appropriate change value at any level of the hierarchy.

6.  Create the following new query:

-- MXAS15-1:  Simple Time Hierarchy on Row Axis
   { [Measures].[Warehouse Sales] } ON COLUMNS,
   { [Time].[Year].[1997].[Q1].Children,
                                        [Time].[Year].[1997]} ON ROWS

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